1. Field of the Invention
The present invention relates to an image display device that is provided with a reversibly rewritable display layer that has the capability to retain images.
2. Description of the Related Art
Due to increased paper consumption in offices, display technology media that can be used in place of paper have attracted attention. Such media include technologies such as electronic paper, which is reversibly rewritable/updatable and has the capability to retain images. This type of electronic paper must fulfill certain requirements, namely, it is necessary that the energy needed to rewrite with this type of electronic paper be small; that the paper be lightweight so as to be suitable for carrying around; and the paper must be highly reliable.
There have been many proposals for this type of electronic paper involving display methods utilizing photochromic compounds that allow for reversible rewriting by exposure to light. For examples of such paper, refer to Japanese Patent Application Laid-Open (JP-A) Nos. 2004-18549, 2004-198451, 2003-131339, and 2003-170627.
Multi-colored photochromic materials are disclosed in JP-A Nos. 2004-18549 and 2004-198451. These materials comprise titanium oxide that support silver particles. When visible light is irradiated on this titanium oxide, the material turns a color corresponding to the color of the visible light. With the technologies disclosed in JP-A Nos. 2004-18549, 2004-198451, an image display medium is provided where the photochromic material including titanium oxide is formed into a thin film formed on the surface of a glass substrate. When making the photochromic material formed into a thin film on the image display medium display color, it is necessary to irradiate visible light rays of a specified wavelength region on the photochromic material of the image display medium.
As shown in JP-A Nos. 2003-131339 and 2003-170627, the irradiation of visible and ultraviolet light on this type of photochromic material is performed with specialized image display devices. This type of image display device specifically includes components such as: a light source with a waveband that makes the photochromic material display colors; an ultraviolet lamp for irradiating ultraviolet light; rollers for conveying the image display medium to the positions where this light source and the ultraviolet lamp are arranged; and discharging rollers for discharging the image display medium irradiated with light from the light source and the ultraviolet lamp to the exterior of the device. Thus the displaying of an image on the image display medium is performed by irradiating visible or ultraviolet light on the photochromic material of the image display medium by an image display device that is provided separately from the image display medium.
With the above-described prior art, a specialized image display device is provided for forming an image on a display medium provided with a photochromic material. Since rewriting and erasure of an image displayed on the image display medium is performed, when writing an image in order to display the desired image on the image display medium, it is necessary to carry the medium to a position where the specialized image display device (i.e., writing device) is arranged. The execution of simple and easy rewriting of an image has thus proven difficult.